Recently, as a solution to environmental problems, hybrid vehicles, fuel cell vehicles and electric vehicles that run by the driving force from a motor have been attracting attention. Such a vehicle mounts a motor as a driving source, and while the vehicle travels, the motor may generate vibration and noise. In view of such a problem, Japanese Patent Laying-Open No. 5-162542 discloses an electric vehicle driving device that aims to realize both improved vehicle installability and reduced noise and vibration. The driving device is characterized in that, in an electric vehicle including a plurality of driving motors, motor bodies are coupled through a vibration control member. The driving device is further characterized in that, in the electric vehicle including a plurality of driving motors, the motor body is mounted on a vehicle body with the vibration control member interposed.
According to the driving device for an electric vehicle disclosed in the laid-open application, even in a type in which motors of the electric vehicle are coupled to each other, vibration generating actions of each other are restrained, whereby transmission of vibration can be reduced. Further, both improved installability of motors and reduced vibration and noise can be attained. In addition, durability of motors themselves, quietness of the vehicle, and stability in running can be improved.
Further, as an electric vehicle having a motor as a driving source, not only a vehicle having the motor on the side of vehicle body but also a vehicle having an in-wheel motor in its wheel has been known.
The vehicle provided with an in-wheel motor, however, has a problem that vibration generated in the in-wheel motor is transmitted to the side of vehicle body. The vibration and noise generated when the motor is driven are in the frequency band of several hundred Hz to several kHz, caused by rotor rotation or gear meshing. Such vibration is particularly notable when the vehicle speed is increased and decreased.
A housing of the in-wheel motor is mounted on a suspension through a ball joint. Between the ball and a receptacle of the ball joint, grease is filled. The ball joint receives torque reaction force of motor when the vehicle speed is increased and decreased. When the ball joint receives the torque reaction force, the ball is brought into contact with the receptacle or a wall surface in the ball joint. When the ball contacts the receptacle or wall surface in the ball joint, degree of transmission of vibration generated in the in-wheel motor through a suspension (that is, lower and upper arms) to the vehicle body increases (in other words, vibration tends to be transmitted easily). As a result, vibration and resultant noise are generated in the vehicle interior, possibly causing sense of discomfort of persons in the vehicle.
At a root portion of a shock absorber or at a mounting portion between the suspension and the vehicle body, a vibration damping member such as a rubber bush is provided. This realizes a structure in which shock or vibration from the road surface is not transmitted to the vehicle interior. The rubber bush, however, corresponds only to input vibration of about 10 to about 15 Hz from the road surface. Therefore, high-frequency noise generated in the in-wheel motor cannot be reduced.
In the electric vehicle driving device disclosed in the laid-open application, the motor is mounted on the side of vehicle body through a vibration control member. Specific technique for preventing high-frequency vibration transmitted from the in-wheel motor to the vehicle body when the vehicle speed is increased and decreased is not disclosed at all.